1. Field of the Invention
The present invention relates to a rolling bearing lubricated with grease and particularly to the rolling bearing for use in a fan motor.
2. Description of the Related Art
A rolling bearing having a retainer made of resin has been mostly used in a motor having a fan on a shaft (hereinafter referred to as fan motor) for use in household electrical appliances such as a vacuum cleaner, a washing machine and a KOTATSU (Japanese foot warmer with frame and coverlet), air conditioning products such as air conditioners for houses and automobiles, a hot-air heater, an air cleaner, and a smoke separator, a hot-water supply device, a personal computer and measuring devices.
In the rolling bearing used in the fan motor, generally an axial clearance gap ratio δa/Da of a diameter Da of a ball as a rolling element to an axial clearance gap δa provided between a pocket face of a pocket of a retainer and a rolling face of the rolling element is set to about 0.08, a radial clearance gap ratio δr/Da of the diameter Da of the ball to a radial clearance gap δr provided between the pocket face of the retainer and the rolling face of the rolling element is set to about 0.1. As a lubricating material, used is a grease obtained by adding a lithium soap base or diurea base thickener to a base oil.
However, in the case where the above-mentioned related-art rolling bearing is used in a low temperature environment, a base oil kinematic viscosity of grease becomes higher so that the base oil having the high kinematic viscosity irregularly flows in the clearance gap between the rolling element and the pocket, resulting in easily generating a collision noise (hereinafter referred to as retainer noise) due to collision of the rolling element and the retainer. Especially in the case of use in a very low temperature environment as much as −30° C., such a tendency becomes further strong.
Further, when a grease contains a large quantity of thickener for making the base oil of grease semi-solid, the grease is liable to be solidified at a low temperature so that the fluidity is lowered to further easily generate the retainer noise.
On the other hand, among the fan motors, as to the rolling bearing used in the fan motor especially used in an air-conditioning product such as an air conditioner, even if the retainer noise in a low temperature environment is a little, there has been the demand toward the reduction of noise. Further, there has been a strong demand toward energy-saving of electric appliances, and the rolling bearing has been expected to be decreased in a driving torque.